Unity dock options / behavior: you can pin applications to the dock by right clicking them and selecting "Keep in Launcher", meaning you'll always have a shortcut available when the application is not running. Also, running applications have an arrow on the left, while the currently active application has an arrow on the right (thus the two arrows on Chrome in the screenshot below):

The dock is scrollable which will be a great advantage for touch devices. To scroll it, hold the dock with your mouse and drag. In the screenshots you'll also notice Google search in the top left corner - that's like a shortcut for Google that will open up a new tab in your default browser with the searched keywords.

You can also re-arrange the dock icons but in a somewhat unusual way. You must drag an icon to the right and then moving it to the new position:

The dock also has a really nice effect for applications demanding attention such as a new Pidgin or Empathy conversation. Unfortunately I didn't get this in the video and a screenshot would be useless so you'll have to see that for yourself.

The applications don't minimize to the dock like you would expect if you ever used a Linux dock or OSX's dock. The switching is done using the Ubuntu logo in the top left corner which resembles to Gnome Shell Activities button yet the behavior is similar to Mac OSX's Expose - which lists all running applications:

One thing missing from the Ubuntu Unity dock is handling multiple windows of the same app - there's no indicator in the dock pointing out how many instances / windows are running for the same application. But you can run Expose for the windows associated with an application by right clicking the application's icon in the dock.

The date has been removed from the Unity interface: only the time is displayed in the panel and upon clicking it, the user can see the date as well as adjust the date/time:

Impressions

I initially wanted to install Unity right away on my netbook as the main interface. But in the current state, Unity - or only Unity without another dock / app switcher - is not usable. There's no way to access applications which are not available in the Unity dock (you can only pin running applications - but to get them to run, you must have access to them somehow, and Unity doesn't provide this for now) so initially you must use something else for a launcher because the Ubuntu logo in the top left corner is used for Expose, not for bringing up a menu. Sure, you could use a terminal to launch some apps, but that's not in the Unity dock by default so if you don't have Gnome Do set up to autostart, it will take you a while before actually running an application.

Another feature I really missed in Unity is panel applets - just like in Gnome Shell - is that you can't add applets to the top panel. Sure, the top panel will be used in the future to hold the mighty Global Menu but for now it's a bit useless and annoying. You can't even right click it (you can, but nothing will happen).

And another option I would have wanted and found that it's missing is creating custom launchers in the Unity dock - that's not possible for now. You also can't change any dock icon.

Finally, a note: if you want to run Compiz using Unity... you can't, just the way you can't currently run it with Gnome Shell. Hopefully this will change in the future.

Here is a video with Ubuntu Unity in action

The video has been recorded in 1080p. You can also watch it @ Youtube.